1. Field of the Invention:
This invention relates to an electromagnetic device for a camera, and more particularly to a release type electromagnetic device for a camera.
2. Description of the Prior Art:
Recent, photographic exposure control apparatus for a camera with an electrically controlled shutter have been designed to operate with low power consumption and, at high speed. In an electronically operated magnetic control device of the release type (hereinafter referred to a "release type electromagnetic device") as shown in FIG. 1, an armature 1 is held in the attracted position by the applied magnetic flux from a permanent magnet 4. When the coils 5 and 6 are electrically energized at a desired time, the magnetic flux of the permanent magnet 4 is cancelled. This cuses the armature 1 to be drawn away from the attracted position.
In the case of the release type electromagnetic device of FIG. 1, though the consumption of electrical energy is relatively low and the response characteristics is improved, there still exist the following disadvantages: In manufacturing the release type electromagnetic device, the end surfaces 2Aa and 2Ba of the yoke 2 must be subjected to a polishing process after the permanent magnet 4 has been fixedly mounted between the two parts 2A and 2B of the yoke 2 by an adhesive agent. Because the spans L of the yoke 2A and 2B are comparatively long, there is a high possibility of subjecting the yoke 2A and 2B to an inclining or twisting effect effect during the polishing process. This may cause the aprellelism between the opposite end surfaces 2Ab and 2Bb to deviate from the allowable accuracy, for example, usually 0.5 micron. Further, the inclining or twisting effect often results in accidental separation of the permanent magnet 4 from the yoke 2.
In other words, the conventional type electromagnetic devices, in spite of their various advantages, are very difficult to manufacture and their production yield is low.